1. Field of the Invention
The present invention relates to a signal sensing circuit, and more particularly, to a signal sensing circuit inside an integrated circuit.
2. Description of the Prior Art
Referring to FIG. 1, an inverting closed-loop amplifier for measuring current is shown. This inverting closed-loop amplifier includes a negative feedback loop, wherein the negative feedback loop has a reference resistor with a reference impedance R. When the negative input of the inverting closed-loop amplifier receives a current input I, the ratio between changes in a voltage output V of the inverting closed-loop amplifier and changes in the current input I is a constant. For example, the potential to which the positive input of the negative feedback loop is coupled is 0, the output voltage V equals to the input current I multiplied by the reference resistor R. Thus, when current is converted into voltage, there will be an effect of the impedance R, that is, the conversion is dependent on the impedance.
If this circuit is implemented in a semiconductor manufacturing process for an integrated circuit, manufacturing process variations may create variations in the impedance. In the same integrated circuit, the characteristic variations of the impedances may be similar, whereas the characteristic variations of the impedances between different integrated circuits may have large differences, possibly up to ±20%.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.